Underwater investigations are conducted for a variety of reasons to include mine hunting, search and rescue operations, bottom mapping, marine life studies, the viewing of maritime accidents and shipwrecks, and environmental investigations. The means for carrying out these investigations are as varied as the types of investigations. For example, in terms of mine hunting, underwater reconnaissance is currently conducted by both manned and unmanned systems, a variety of which will described briefly below.
The use of a dedicated mine hunting ship (DMHS) is the traditional method of clearing mines. However, the DMHS is an expensive piece of equipment and is expensive to run owing to the costs associated with the wages of the ship's crew. The DMHS requires the use of valuable manpower that could be more productively used in other tasks. The DMHS also uses valuable harbor space due to its size. The mine hunting exercise itself cannot be made in a timely manner due to the ship's lack of speed. Furthermore, the imminent hazards associated with placing a ship and its personnel into a minefield make this method of mine hunting the least attractive.
A helicopter towed sensor (HTS) has become a more available and quicker method of mine hunting. However, the HTS is plagued by short duration mission capability due to a helicopter's fuel requirements. The complexity of launching and recovering the equipment from the helicopter prevents this approach from being performed at night. Finally, the inherent instability of helicopter flight can make the HTS mission an extremely dangerous one.
Even more recently, a remote vehicle towed sensor (RVTS) involves the towing of a sensor behind a semi-submersible vehicle. However, the semi-submersible vehicle must be powerful enough to overcome the large drag forces associated with a tow cable. The drag on the tow cable also limits the speed of the RVTS resulting in long missions. The tow cable also inhibits maneuverability. Further, in order to keep the tow cable properly tensioned, the RVTS must make very large and time consuming turns.
Another unmanned option utilizes an unmanned underwater vehicle (UUV) equipped with onboard sensors. However, this type of system is not capable of completing the mine hunting mission with the current capabilities of UUVs. The power density of such a craft would require it to travel at extremely slow speeds for the entire time that it is on a mission. The fact that the craft is underwater for the entire mission also prevents communication with the host ship. This lack of communication would require the host to wait for hours or days before critical information is received. Another drawback of this type of system is endurance. That is, current battery technology does not give this type of system enough endurance to complete longer missions. Still another problem is the inaccuracy of a UUV's inertial guidance system. Specifically, the inaccuracies in an inertial guidance system multiply over the course of the mission until the craft is so “lost” that any information that it recovers would be useless.